22589 Biogas in Practice AW:1 - Aylsham Growers Renewables · 2013-04-26 · KWS funds what is...

Biogas in Practice

Bioenergy

22589_Biogas in Practice_AW:1 21/6/12 17:43

Biogas CroppingFor the farmer developing a biogas operation, high output feedstock crops are anecessity. At the same time, for the grower with a plant in the near neighbourhood,biogas cropping represents a useful source of income.

While it would be easy for both to compromise and utilise currently grown crops within a biogas operation, this would result in a reduced methane yield.

Continental experience shows clearly that the selection and growing of crops for biogasneeds as much careful thought, planning and husbandry expertise as cropping for food.

This book – a follow-on from our ‘Growing Crops for Bioenergy Guide’ – aims to provide biogas entrepreneurs, and those who support them, with the latest advice onbiogas cropping in the UK.

It examines the potential of a range of crops and crop mixes as feedstocks in a biogasplant – providing advice on which crops will provide maximum methane yields per tonneof dry matter and, more importantly, per area of cropped land.

It then looks at the prospects for these crop mixes across UK conditions and theirsustainability in a typical rotation, before finally assessing the individual needs of thosecrops most suited to drive methane yield.

The guide draws on the research and experiences of our colleagues in continentalEurope, but also the expertise of current biogas producers in the UK, with whom we have a close working relationship.

KWS funds what is believed to be the only long-term energy crop breeding programmesacross Europe. Our focus is on providing varieties that maximise methane outputs andare sustainable in a UK biogas rotation and we look forward to helping you do likewise.

John Burgess Simon WithefordMaize Product Manager Sugar Beet Product Manager

Contents

Biogas Cropping 3

Feedstock Prospects 4

The Rotational Mix 7

Geographical and Soil Type Limitations 7

Rotational Balance 8

Other Issues 10

Digestive Values 11

Individual Crop Agronomy 12

Geographical Potential 13

KWS Energy Maize – Hybrid Characteristics 17

Agronomics 18

Energy Beet 22

KWS Breeding Programme 32

Wholecrop Hybrid Rye 33

Ryegrass 37

Summary 38

Notes 39

Biogas in Practice 32 Biogas in Practice

22589_Biogas in Practice_AW:1 21/6/12 17:43

Feedstock ProspectsIdeally biogas production would benefitfrom a consistent mix of feedstockmaterials, chopped and blended to ensure optimum methane yield.

In practice, Anaerobic Digester (AD) unitsmay also rely on a proportion of foodwaste. This is largely beneficial to theenvironment; however as a singlefeedstock, food waste and industrial by-products can present challenges in the consistency of gas output andtherefore income.

A base feedstock from break crops, or energy crops grown as part of a farmrotation, is an ideal solution for farmersand helps provide an alternative incomestream alongside standard combinableand commodity crops.

Yield is the overriding consideration forefficient energy crop production. The keyis to use a feedstock mix that allows the digestion process to function effectively,

Spe

ed o

f fer

men

tatio

n (re

l.)

5 30 60 70 90 100

Biogas: relative fermentation characteristics by crop

Retention time for substrate fermentation (days)

sugar (Mono. Disaccharide)

starch (Polysaccharide)

proteinpectin (Polysaccharide)

hemicellulose (Polysaccharide)

cellulose (Polysaccharide)

Beet (5-10 days) Maize, Sorghum, Hybrid Rye (50-90 days)

lignin

and maximise methane output, given thesize, layout and capability of the operation.

The digestion rate of different feedstockswithin a biodigester varies from two daysto two months. Material that has a highlevel of sugar or starch is quicker toferment than feedstocks which have more lignin or cellulose (Figure 1).

Figure 1. Relative FermentationCharacteristics

Thus, material like energy beet will have a shorter retention time in the digester andrelease more gas over a shorter period of time than wholecrop cereals or maize.

However, in terms of total methane yield; both wholecrop cereals and maize, while slowerto release gas, can be just as effective as energy beet (Table 1).

Each individual feedstock component has advantages and disadvantages

Table 1. Feedstock Characteristics

Feedstock Fresh Weight Dry Biogas Yield Methane Methane YieldYield (t/ha) Matter % m3/t (Fresh) Conversion m3/t (Fresh)

Energy Maize Silage 60 27-31 200 53% 105

Ensiled Beet 78 22-24 180 55% 99

Fresh Beet 78 22-23 170 51% 86

Wholecrop Cereals* 35 33-36 200 54% 108

Grass Silage 25 25-28 160 53% 90

Sunflower Silage 12 22-26 105 57% 60

Cattle Manure - 8-10 24 40% 12

Data source: KWS SAAT AG

Feedstock Advantages Disadvantages

Maize High methane yield/ha Relatively slow retention time Easy storage and feedout

Energy Beet Highest possible yield/ha Needs careful storage Fastest possible retention time

Grass High DM – but 20% lower gas Low methane yield/ha yields/t fresh weight than wholecrop cereals or maize

Rye High wholecrop yield with high DM Lower methane yield/ha Good for drought prone areas Good feedstock partner for maize

Manure Useful starter and mixer product Low methane output – so may not suit larger plants


*Wheat, Rye, Barley, Triticale. Data source: KWS SAAT AG


22589_Biogas in Practice_AW:1 21/6/12 17:43 Page 4

Table 2 illustrates some examples ofpotential mixes in the biogas plant. This shows that, per tonne of fresh weightproduced, the most effective mixes formaximum methane yield should comprisemaize and wholecrop cereals. However,when you look at the methane yield perhectare, utilisation of 10-30% energy beetalongside these two crops has a positiveeffect on output from the land area.

Care does need to be taken to ensure that the viscosity of the mix enables good functionality of the plant. So called‘wet’ or ‘dry’ plant designs often specifyfeedstocks to ensure the retention timeand buffering capacity is adequate.

The fast conversion rate of the beet helpsto buffer the gas production, raising thepH inside the plant, encouraging bacterialconversion of the complete feedstock tomethane. Furthermore, beet produces a cleaner source of methane than otherfeedstocks which enables more efficientconversion from methane to electricitythrough the combined heat and power(CHP) unit, or biomethane.

Plant operators will also find that there are significant benefits from the synergiesprovided from using beet. Such synergiesare difficult to quantify and will vary withplant type. However, continental experiencestrongly suggests that use of wholecropcereals with maize does provide a higheryield per tonne of material than maize alone.

The Rotational MixIt is important that whatever crops are selected across the rotation, when used incombination they provide secure yields every season and so do not limit the supply of feedstock.

Some low risk crops – e.g. grass and wholecrop cereals – are well suited to UK-wideconditions on all bar the driest and wettest sites respectively, but their yields/ha do not match those of maize or beet.

GrassRoughly 70% of the UK cropped area is down to grass, either as a crop or inpermanent pasture predominantly in higher rainfall western regions.

Grass can be grown in drier regions but it may be feasible to take only one cut,coinciding with peak yields in late May or early June.

Elsewhere 2-3 cuts could be possiblegiven a relatively intensive managementapproach.

Wholecrop CerealsWhile wheat or barley will suit mostregions, crops such as hybrid rye areparticularly well suited to drier regionssuch as the South East and East ofEngland.

Hybrid rye, with its prolific straw length, will also be a strong performer in traditionalcereal growing regions as an alternative towheat or barley. Triticale is an alternative.

**Assumes ensiled beet. †Doesn’t take into account synergies of the various feedstock mixes. Data source: KWS SAAT AG

Geographical and Soil Type LimitationsMaizeMaize requires high temperatures over a long summer period for maximum yieldand maturity.

Most specialist energy hybrids have a very high dry matter yield but are relativelylate to mature. So while these crops willsuit favourable sites in current maizegrowing regions, earlier hybrids will berequired if production is to be consideredfurther north.

Energy BeetThe only limitation to energy beetproduction is the ability to be able to get on the ground to plant and thenharvest the crop.

Thus, geographically, UK growers couldgrow energy beet across the UK, butproduction is more limited on those soilsthat are still at field capacity in mid Apriland/or return to field capacity at aroundthe end of October.

Table 2. Potential Crop BasedFeedstock Mixes

Example Methane MethaneFeedstock Yield m3/t Yield m3/ha Mixes (Fresh) (Fresh)†

Maize 100% 105 6300

Maize 90% + 100 6360Beet** 10%

Maize 70% + 96 6480Beet** 30%

Maize 70% + 112 5544Wholecrop 30%

Maize 40% + 106 5724Wholecrop 30% + Beet** 30%



MaizeMaize suits most rotations includingcontinuous cropping, though care needs to be taken when grown in closeassociation with cereals due to theincreased spread and risks of Fusarium.

Late harvesting can be an issue, but inmost situations growers should be able to follow with an autumn sown wholecropcereal or grass crop.

When considering planting energy beetafter maize, growers will need to considersoil conservation and cross complianceissues as a consequence of leaving maizestubbles over winter.

Energy BeetLike maize, highest yields of energy beetcan be taken from lifting the crop as late as possible with yields peaking in mid-late November. In milder parts of theUK the crop could be left in the groundover winter.

Rotational BalanceClose cropping of energy beet should be avoided or growers could create a build-up of Rhizomania, or Beet CystNematode (BCN). The crop shouldn’t be grown at a greater interval than one in three.

GrassGrass is a highly flexible crop. Some mayconsider planting it after an autumn liftedbeet or maize crop and then taking a cropoff it in the following May, prior to drilling a maize or beet crop.

Wholecrop CerealsApart from the limitations of croppingcereals with maize, winter or spring cerealvarieties can be utilised to suit rotationalrequirements.

In the extreme South, it may be feasible to cut a wholecrop cereal in May and then follow with a later planted, very earlymaize hybrid.

Table 3. Example Rotational Performance

Maize Grass Cereals Energy Beet

Highly suitable Less suitable

Potential Example Rotation Likely Situation/Location Combined 3 Year and Yield Performance Yield (t/ha)

Year 1-3 Maize (55t/ha) Favourable conditions – eastern 165half of England – suits large 1 mWplus plants

2 Year Rotation: Favourable conditions – where 127Year 1 Maize (55t/ha) beet doesn’t suit (e.g. vegetable Year 2 Wholecrop Cereal (30t/ha) production regions) – suits 1 mW plants

Year 1 Maize (45t/ha) Ideal for livestock areas or smaller 100Year 2 Wholecrop Cereal (30t/ha) 650-750 kW biogas installationsYear 3 Grass† (15t/ha)

Year 1 Beet (70t/ha) More sustainable rotation – suits all 155Year 2 Wholecrop Cereal (30t/ha) biogas plant sizesYear 3 Maize (55t/ha)

Year 1 Beet (70t/ha) Where maize cropping is not 130 Year 2 Wholecrop (30t/ha) possible – e.g. Northern Britain Year 3 Grass – 2 year ley (30t/ha)

Table 3 illustrates the likely yield over some example three year rotations ofbiogas crops.

Continuous maize produces the highestyields that will ensure a good supply ofmaterial for larger biogas plants (1 mWand above).

A rotation where maize is joined bywholecrop cereals and energy beet maybe a better approach and one that is more sustainable.

Finally, the use of energy beet, wholecropcereals and then grass will also provide a more tenable yield of material for those in Northern Britain where maize croppinghas been less successful.

†Assumes first cut grass silage only. Data source: KWS SAAT AG


Geographical Suitability


Other IssuesGrowers need to ensure they maintaingood soil health and minimise the risks of erosion and soil loss. Here, the use ofcover crops after later harvested maizemay be necessary – and could provideadditional material for the digester.

Care needs to be taken to ensure that the use of any slurry and digestate fits in with cross compliance guidelines.Spreading or injecting of digestate wouldbe best in the spring immediately prior todrilling of a spring crop.

Growers should also consider the effectsof a mix of winter and spring crops withinthe rotation. A period of fallow is beneficialand in certain situations, particularly wheregrass weed control is increasingly difficult,the use of a spring crop can help growersget on top of grass weeds.

Finally, where large areas of mono-cropping, e.g. maize are proposed, there will be a noticeable change in thevisual appearance and often the aestheticappeal of the countryside. This does need to be considered. To counter this,growers can consider catch crops orheadland mixes of sunflowers, phacelia or wildflowers to offset this effect.

Digestate ValuesThe nutrient content and the value of thedigestate also vary according to rotationalfeedstock mix (Table 4).

However, whatever the cropping patternand subsequent analysis, significantamounts of N, P & K plus valuable rates of other nutrients can be returned to soilswhen digestate is spread at reasonablerates/t (Table 5).

Long term use of biodigestate providessignificant improvements in soil physicalcondition, workability and fertility.

Table 4. Feedstock and Digestate Value

Table 5. Typical Digestate Nutrient Value

The tables in this and the previous section of this guide use examples of some typical crop and feedstock mixes.

KWS UK has prepared an interactive guide which enables growers tocompare the effects of specific crop mixes on dry matter, biogas andmethane yield.

As part of our support service, we would be pleased to run through thesewith you and to examine the effects of different crops in your individualsituation.

Feedstock Digestate Value (kg/t)

N P K

Maize Silage 3.7 2.4 4.5

Ensiled Beet 2.2 1.0 2.2

Fresh Beet 1.2 0.6 1.9

Wholecrop Cereals* 5.9 3.7 7.3

Grass Silage 5.3 2.9 9.4

Sunflower Silage 4.5 2.2 5.7

Cattle Manure 4.5 3.6 7.9

*Wheat, Rye, Barley, Triticale. Data source: KWS SAAT AG

kg/t (Fresh) Potentially Available (Spread at 40 t/ha)

N 4.7 113kg/ha

P 1.8 43kg/ha

K 5.2 125kg/ha

Mg 0.8 19kg/ha

Ca 2.1 50kg/ha

S 0.34 8kg/ha

Analysis based on 75% maize & 25% fresh manure.Data source: KWS SAAT AG



Individual Crop AgronomyEnergy Maize

Geographic PotentialThe KWS North European maize breeding programme continues to develop, assess and introduce maize varieties that are adapted to UK conditions.

Earlier maturing hybrids that are more suited to northern, colder and heavy soil sites are being developed and these are helping extend successful energy maize productioninto new regions.

Physiological Requirements

Germination Soil Temperature >8°CYoung Plant Development Soil Temperature >10°C

<10°C – leaf tissue becomes shrivelledLate frosts of -3°C or below lead to plant death

Maturity Autumn temperatures of 6.5°C or below, halt growth

Advantages Disadvantages

High DM yield Later harvest – soil damage and risk of compaction

Black grass control and wide herbicide spectrum Following winter crop options can be limited

Low cost per tonne Ideally needs to be balanced with other cropsubstrates to encourage a faster retention time

Can be grown continuously

High yield potential on lighter land

High biogas yields



Our work, and that of our researchpartners, has clearly shown that biomassyield/ha correlates strongly with biogasproduction and is the key to high biogas yields.

Research from the University ofHohenheim, for example, confirms that the key to high methane yield is dry matter and that starch content and plantdigestibility have only a minimal effect on methane output.

The study, which analysed the gas outputfrom 10,800 plots testing 600 hybrids and 300 inbred maize lines confirmed adirect correlation between dry matter yieldand methane output.

This relationship is very strong with littlevariance around the straight line plot andstatistical analysis giving a near perfect0.98 R2 correlation – i.e. over 98%. In alltests, all hybrids produced a narrow bandof 300-330l methane/kg of dry matter.

Energy Maize BreedingKWS breed hybrids for biogas that maximise yields and provide a low production cost per tonne. High cold tolerance and vigour, standing ability and an improvedearliness/yield ratio are all key attributes of our material.

Maize grown for biogas requires different characteristics compared to maize for forage.Forage maize produced for ruminants (dairy and beef cattle) requires high energy contentin the form of starch and the appropriate dry matter content to encourage feed intake.For energy varieties starch content is less important than dry matter production.

Maize grown for biogas focuses on maximum yield, and a lower dry matter content, toencourage fermentation. Using a short chop length will help speed the process. Maize will have a long retention time of up to 100 days.

Spe

cific

met

hane

yie

ld l/

kg o

rgan

ic D

M

100

150

200

250

300

350

0 5 10 15 20 25 30 35 40

Starch (%)

Mas

s ty

pes

Hig

h qu

ality

type

s

Soil Type Advantages Disadvantages

Light Warm and easy to work Droughty and liable to erosionAllows earlier drilling of later, higher yielding varieties

Medium Good water supply, fertile and easy to work

Heavy Good water supply, fertile Slow to warm, dense/compactLater drilling of earlier varieties is recommended structure, silts are likely to cap

Organic Good water supply, fertile Slow to warm, low pH (<7), suffer from late frost

Forage Maize (Cattle Feeding) Energy Maize (Biogas Output)

Minimum methane production in the rumen Maximum methane production per ha

Dwell time: 5-10 hours Dwell time: 50-100 days

Maximum feed value Maximum biomass (yield and dry matter)(starch and whole plant digestibility)

Sufficient dry matter for feed intake (30-35%) Sufficient dry matter for fermentation (27-31%)

Long chop length for rumen degradability Short chop length for surface area (7-10mm)(12-15mm)

Met

hane

yie

ld (m

3 /ha

)

4000

6000

8000

10000

0

100

150

200

250

Dry matter yield (dh/ha)

300

Data source: University of HohenheimData source: University of Hohenheim

Chart 1. Starch and Methane Yield Chart 2. Dry Matter Yield and Methane Yield


Soil and Site Potential

A standard forage maize hybrid (left) and a high biomass energy maize (right)


No correlation

Strong correlation


Gas OutputThe following factors all play a critical rolein optimum methane yield, and all aredirectly linked to the management of thecrop in the field and at harvest.

• Harvest date (lignin %, dry matter %,chop length)

• Storage (fermentation, absence of air)• Dwell time (substrate mix, plant design)

Shorter chop lengths (typically 7-10mm)are desirable, so as to maximise surfacearea and assist rapid substrate breakdown.

Clamping is also critical; securing anairtight seal will encourage maximumclamp stability and minimise losses.

Variety Selection• Variety selection should be based on

the estimated level of heat units and field and soil conditions

• The FAO number is a measure of therelative earliness of the variety andrepresents the number of days a variety will take to reach a specific grain moisture

• The earliest varieties, now morecommonly grown for fodder maize inmarginal conditions, have low FAOratings of around 150-160. They takefewer days from planting to maturity andrequire up to 20% fewer heat units thanmedium early hybrids but have a lowerabsolute yield potential.

• Over recent years yield development hasbeen greater in energy maize than silagemaize.

• Very high fresh yield potential (55-65t/ha) • Large structured hybrids with excellent standing ability • Safe maturity for the majority of mainstream sites (28-31% dry matter) • Moderate stay green (recommended chop length 7-10mm)

Fres

h yi

eld

t/ha

Yield potential by FAO number

40

30

50

60

70

170

160

190

220

240 25

0 260 26

0

Silage MaizeEnergy Maize

Fresh Yield (t/ha)

Dry Matter (%) & DM Yield (t/ha)

27% 28% 29%* 30%* 31%* 32% 33%

45 12.2 12.6 13.1 13.5 14.0 14.4 14.9

47 12.7 13.2 13.6 14.1 14.6 15.0 15.5

49 13.2 13.7 14.2 14.7 15.2 15.7 16.2

50 13.5 14.0 14.5 15.0 15.5 16.0 16.5

51 13.8 14.3 14.8 15.3 15.8 16.3 16.8

53 14.3 14.8 15.4 15.9 16.4 17.0 17.5

55 14.9 15.4 16.0 16.5 17.1 17.6 18.2

57 15.4 16.0 16.5 17.1 17.7 18.2 18.8

59 15.9 16.5 17.1 17.7 18.3 18.9 19.5

61 16.5 17.1 17.7 18.3 18.9 19.5 20.1

63 17.0 17.6 18.3 18.9 19.5 20.2 20.8

65 17.6 18.2 18.9 19.5 20.2 20.8 21.5

67 18.1 18.8 19.4 20.1 20.8 21.4 22.1

69 18.6 19.3 20.0 20.7 21.4 22.1 22.8

71 19.2 19.9 20.6 21.3 22.0 22.7 23.4

73 19.7 20.4 21.2 21.9 22.6 23.4 24.1

75 20.3 21.0 21.8 22.5 23.3 24.0 24.8

Dry Matter Yield/ha = Methane Yield/ha

Yield Reference Table

Forage Maize (FAO 150-210) Energy Maize (FAO 220-260) *Optimal harvest dry matter

Fres

h yi

eld

t/ha

Yield progress

20

0

60

100

120

80

40

2002

2004

2006

2008

2010

2012

2014

2016

2018

2020

Silage MaizeEnergy Maize

FAO Maturity Yield Potential

170 Short season/ ++ Late Drilling

220 Early +++

250 Mid Early +++++

260 Late ++++++

Energy PotentialWith its versatility, very high fresh yieldpotential and relatively easy cultivation,maize has become the main substrate for the ever increasing number of biogasplants, particularly in Germany, andelsewhere in North West Europe.

Energy ForageMaize Maize

Fresh Weight Yield 60 45(t/ha)

Dry Matter % 27-31 28-35

Biogas Yield m3/t 200 200Tonne (Fresh)

Methane Conversion 53% 53%

Methane Yield m3/t 105 105Tonne (Fresh)

Methane Yield m3/ha 6300 4725

KWS Energy Maize – Hybrid Characteristics

Dat

a so

urce

: KW

S S

AAT

AG




AgronomicsDrilling, Seed Rates and Row WidthTrials have established a methane yieldgain from closer rows. Typically thestandard row width of 75cm (30”) used for forage maize can be reduced to 50cm(20”) or 37.5cm (15”).

Closer rows produce a denser crop with higher fresh weight yields and tend to promote a slightly faster dry down at harvest. Consideration should be givento deeper and earlier drilling, where soilsare lighter.

Considerations: • Yield response is highest with earlier

varieties (FAO 200>) • Energy maize suits lighter soils and

earlier drilling – drill deeper into moistureif needed

• Earlier varieties will have a fast dry-downat harvest leading to an increased drymatter%

• There is an increased risk of lodging/plant competition with late varieties (FAO240<), so ensure you select an appropriatevariety split, for your conditions

Air and heat

Free drainingwarm soil

Crumbstructure

Heat reflection

Compacted seed bed

Cold seedbed, poor nutrient supply

Soil StructureMaize requires a well structured topsoil and well prepared seedbed. Compaction has a marked effect on crop growth and yield.

Nutrient Use Maize has a high nutrient demand, particularly for potash. Assess soil reserves and tailor fertiliser applications to match site/field potential, for maximum yield.

Nutrient Removal

Recommended Seed Rates

*1 Unit = 50,000 seeds


Typical Fertiliser Recommendations

Deposition Distance (cm)Plants/ha (acre)

at 75cm (30") at 37.5cm (15")Units*/ha (acre)

95,000 (36,000) 13.3 26.7 2.0 (0.81)

100,000 (38,000) 12.7 25.3 2.1 (0.85)

105,000 (40,000) 12.1 24.1 2.2 (0.89)

110,000 (42,000) 11.5 23.0 2.3 (0.94)

115,000 (44,000) 11.0 22.0 2.4 (0.98)

120,000 (45,000) 10.6 21.1 2.5 (1.00)Harvest Date FAO Drilling Fresh Nutrient Removal (kg/ha)

Maturity Order YieldPotential N P K

Early (mid Sept) 170-200 Last 45t/ha 110 75 210

Mid (late Sept) 220-240 Mid 55t/ha 125 85 230

Late (mid Oct) 240-260 First 65t/ha 165 95 270

Rate (kg/ha) Timing

Nitrogen (N) 100-150 Pre emergence

Phosphorus (P) 80-110 50kg/ha prior to drilling the rest at drilling

Potassium (K) 250-350 Autumn or spring

Sulphur 20-30 To the soil before drilling

Magnesium 40-60 To the soil before drilling



Herbicide UsePre-emergence and post emergenceapplications should be used to minimiseweed competition which can significantlyreduce early growth. Effective utilisation of maize herbicides will help provide good grass weed control, effectivelyboosting control of problem weeds suchas black grass or annual meadowgrasswithin a following cereal crop.

Fungicide RequirementEyespot is increasingly an issue, particularlyin cool, wet summers and in regions wheremaize crops are more concentrated andgrown in tighter rotation.

At the same time be aware that thedisease control and physiological benefitsof this chemistry could delay both maturityand harvest.

Later maturing hybrids (FAO 200 or later)are considerably less susceptiblecompared to early maturing hybrids (FAO 150-180).

Harvest, Maturity and ClampManagementWhen considering the total cropped area,growers should take into account the needfor a wide drilling and harvesting window.The key is to secure high yields and theright level of plant dry matter (27-31%).

Lower dry matter levels increase the risksof leaching losses in the clamp – higherlevels increase the risk of moulds andspoilage on the clamp face and reducedmethane yields (see graph).

Met

hane

con

cent

ratio

n (C

H4/

Kg

DM

)

Optimal harvest window

50

0

150

250

300

200

10010 15 20 25 30 35 40 45 50

CH4/Kg DM

Harvest dry matter (%)

Variety Planning

Total Cropping Suggested % Area (ha) Breakdown of Maturity

Early Mid Early Late

150+ 40 35 25

350+ 35 30 35

550+ 35 25 40

Increasing the proportion of later maturinghybrids provides a wide window forestablishment and harvesting capacity.

Aim for a chop length of 7-10mm tomaximise compaction in the clamp andoptimum surface area for bacterial activity.





Fresh Dry Biogas Methane Methane MethaneWeight Yield Matter % Yield Conversion Yield Yield

(t/ha) m3/t m3/t m3/ha(Fresh) (Fresh)

Energy Maize 60 27-31 200 53% 105 6300

Sugar Beet* 70 22-24 180 55% 99 6900

Energy Beet* 78 22-24 180 55% 99 7722

Energy Beet

Geographic LimitationsEnergy beet is suitable for cultivation across most of the UK.

It has a low transpiration rate – around 300-500l of water/kg dry matter – and canwithstand periods of drought.

Optimum yield requires 180-220 days growth and 2500-2900 accumulated °C heat units.

Optimal germination occurs when soil temperatures reach 5°C and above.

Sunny days and cool nights during August/September provide the highest yields, helping to maximise dry matter production and root weight.

Energy Potential

Biogas beet is one of the most highlyefficient crops by land area in terms ofsustainability and maximum methaneoutput. KWS’ energy beet feature muchhigher dry matter yields than beet grownfor sugar.

The sugar in biogas beet ensuresextremely fast fermentation – usually inless than 14 days. Maize, in comparisontakes 50-90 days. This makes energy beet an ideal partner for maize or wholecropcereals/grass. Furthermore, 95% of thecomplete beet plant can be converted into biogas.

By using a mix of both maize and beet –with beet as the faster fuel conversionsource – producers can sustain high loadsand methane production in the biodigesterover a prolonged period.

The fast conversion rate of the beet helpsto buffer the gas production, raising thepH of the biodigestate mix, encouragingbacterial conversion of the completefeedstock to methane.

Beet also produces a cleaner source of methane than other feedstocks which enables more efficient conversionfrom methane to electricity through thecombined heat and power (CHP) unit.

AgronomicsAs with fodder or sugar beet, a three yearrotation is advisable. More regular growingof beet will lead to increasing problemswith soil pests and diseases.

In particular, be aware that beet cystnematodes are also hosted by the oilseedrape crop, so growing energy beet andoilseed rape in the rotation could see thepest proliferate.

Biogas producers looking to grow beet will need to ensure they have acomprehensive soil managementprogramme that restructures the soil.

Beet is particularly sensitive to soilcompaction. If following cereals, deeploosen or plough the ground prior to winter and allow it to weather down before preparing a seedbed in the spring.On light land a plough and press prior towinter may allow drilling straight ontoground in the spring.

Soil structural damage is likely to be worse when beet and maize are grown in the same rotation. Both crops can beharvested when soil conditions are lessthan ideal leading to subsequent structuraldeterioration.


Suitable for UK soils Relatively high production and processing cost

Established agronomic knowledge Requires a relatively wide rotation >3 years

Consistently high DM yields Storage requires careful clamping

Complete crop can be used

Very fast bio-digestion

High and clean methane yields


*Assumes ensiled beet


Plant spacing

(cm)

Units/ha*

45cm RowsUnits/

ha*

50cm Rows

Target based on 45cm rows – 000’s

Target based on 50cm rows – 000’s

60% 70% 80% 90% 60% 70% 80% 90%

15 1.48 88 104 118 133 1.33 80 93 107 120

16 1.39 83 97 111 125 1.25 75 88 100 113

17 1.31 79 92 105 118 1.18 71 82 94 106

18 1.23 74 86 98 110 1.11 67 78 89 100

19 1.17 70 82 94 105 1.05 63 74 84 95

20 1.11 67 78 89 100 1.00 60 70 80 90

21 1.06 64 74 85 95 0.95 57 67 76 86

Best practice when cropping beet aftermaize may be to leave land uncultivatedover-winter and wait for soil conditionsbelow any soil pan to dry in the springbefore deep loosening and restructuringthe ground. Rough tining may be requiredto reduce erosion risks or potential soilloss from maize stubble.

However, energy beet production fits inwell alongside cereal production, includingthe use of hybrid rye. Energy beet caneither follow early lifted crops of rye, or ryecan be planted immediately post lifting ofthe beet.

Seedbeds need to be well structured,ensuring sufficient seed to soil contact to enable good moisture conservation for fast germination and emergence.

Sugar Beet Drilling Table

Fertiliser GuidelinesEnergy beet requires relatively low supplies of nitrogen and phosphorus, but utilises a significant amount of potassium. Base requirements on soil analyses and take intoaccount expected yield and uptake.

Potash is best applied prior to planting,taking care to avoid a high salt concentrationaround the seed, which will impact ongermination. Fertiliser timing also needs totake into account the risks of leaching onlighter land.

N requirements should be assessed based on N-min tests prior to drilling inFebruary/March. Typical N-use is around80-120kg/ha with the nitrogen appliedearly to promote early crop growth. Careshould be taken not to use more than100kg/ha at any one time as this can leadto salinity issues.

Even if manure or digestates are used asthe main source of N for growing energy

beet, trials suggest that using 20-30kg/hof mineral fertiliser-N is important to ensuregood availability and to promote earlygrowth and establishment.

Compared to growing beet for sugar,amino-N and other impurities (e.g. K andNa content) are not important so growerscan use additional fertiliser to push freshweight yields 10-15% higher than theysecure with conventional varieties whilekeeping within N-max limits.

Boron and manganese are keymicronutrients and foliar applications will be needed where deficiencies are likely or seen.

Data source: LUFA Rostock

Target P2O5 Requirement K2O Requirement MgO RequirementYield (kg/ha) (kg/ha) (kg/ha)

60t/ha 110-120 450-470 90-100

70t/ha 130-140 520-550 100-120

80t/ha 150-160 600-650 120-130

Optimal plant population (85,000-95,000 plants/ha) *1 unit = 100,000 seeds


Beet is particularly sensitive to soil acidityand soils should be limed to pH 6.5-7.Slightly alkaline soils are less of an issue,but care should be taken not to restrictavailability of nutrients such as phosphorus,manganese and magnesium. On peats,aim for a pH of 6-6.5. Drill at 2-3cm depthwhen soils have warmed up to at least 5ºC in March or the beginning of April.

Bolting is less of a concern with energybeet, particularly when taking the wholeplant, so cooler temperatures are less ofan issue than they are with sugar beet.Early sowing in regions with a high risk of late frosts should be avoided as beetcotyledons can be damaged.

Care should be taken to avoid drilling onland likely to cap or slump if heavy rainfallis likely to occur within the next 24 hours.

To achieve maximum dry matter yield, aim to achieve a stand density of 80,000-100,000 plants/ha using a seed rate of110,000 seeds/ha (11 units/ha).


Energy Beet Nutrient Removal

Data source: Adapted from Sugar Beet ReferenceBook 2010, BBRO

Seed treatments should be selected tomatch regional needs and minimise risksfrom soil pests and aphids.

Weed control is essential. Pre-emergenceand post-emergence applications shouldbe used to minimise weed competitionwhich can significantly reduce early growthand canopy closure, thereby restrictingyield production.

Powdery mildew and rust are the keydiseases and maintaining a disease freecrop during the summer maximises cropoutput and dry matter yield. If crops are tobe left to bulk for as long as possibleduring the late autumn and winter, thengreen leaf retention is particularly importantto maximise sugar and dry matter yield.

As a result, the output of these specialisthigh dry matter biogas beet varieties isaround 400 l/methane per tonne of drymatter – approximately 100 l/kg dry mattermore than that of specialist biogas maize varieties.

Care does need to be taken with dirt tarelevels. German operators suggest a dirttare of 5-8% causes no problems, thoughthis tends to be soil type dependent.

Silt and clay soils tend to stay in solutionand move through the digester with thedigestate, whereas sand particles will drop to the bottom of the liquor and maynecessitate the use of sand traps to collectand remove soil and sediment. A numberof modern AD plants will now have inbuiltsediment removers to alleviate this issue.

Other approaches are to mechanicallyclean beet at loading or to use specialistbeet washing equipment prior to ensilingthe beet.

70t/ha Crop

Tops + Crowns Tops + CrownsPloughed Taken Offin kg/ha kg/ha

N 98 280

P2O5 42 91

K2O 126 329

NaCl 35 315

MgO 28 49

CaO 119 168

SO3 70 112

‘Topped’Beet Yield

‘Topped’ Beet Yield + Crown

Energy BeetWhole Plant Yield

7770t/ha ++5+5+ -12% ===7= 8t/ha

HarvestingBy utilising the whole beet plant, including the leaves, relative gas productivity for biogas beet compared to maize rises to 143%.

While it is not always practical to harvest the leaf as well as the root due to liftingmachinery limitations, the leaf material does contribute to the total energy harvested.



Introduction:Storage systems need to be designed and managed to ensure provision of top qualityfeedstock across 12 months. While energy beet can be fed fresh into the AD plant, after around three months beet will start to deteriorate if left open to the elements.

Biogas Process

In fact, ensiled beet will work faster in theAD plant as the ensiling process moves through three of the four steps to methaneproduction, whereas fresh beet willundergo all four processes in the AD plant.

Key requirements are minimal storagelosses from a storage system that ispractical, easy to manage and costeffective. Systems that store whole beet as mashed pulp have been tried and fitmost criteria, though losses from thismethod may be excessive and often as high as 25-50%.

Beet can also been stored in ‘Agbags’which have generally proven to beexpensive and impractical.

Another option is to mix maize silage and whole or chopped beet into the clampat harvest time. The benefits of this arethat the beet runoff is absorbed by thehigh dry matter maize. However, this cannecessitate the beet being harvestedearlier than is optimum for yield and when feeding from the clamp into thedigester you cannot be certain of thevolumes of each component being fed at any one time.

Experience has taught us that ensilingwhole beet for storage meets most of the requirements and that satisfactorystorage is best achieved by following theguidelines below:

Firstly, it is important to minimise the levels of dirt tare and stones in the clamp.While the harvesting, transport andensiling process helps to reduce the levelof soil in the clamp, washing of the beet is an option. Washing may either be a wet or dry process depending on soil type and conditions at harvesting.

Generally a heavy clay based soil will havehigher dirt tares which will be even higherin wet conditions. Allowing the beet to dryafter lifting for a period of time, if possible,and then running over a cleaner loader willremove the majority of this soil. Likewise a sandy based soil, which typically willhave lower dirt tare and can be cleanedsatisfactorily with a cleaner loader.

Some AD plants now have sumps orsediment removers to deal with excessivedirt tare in the plant.

Stone removal is the most importantprocess as stones will impact on chopping

and moving machinery. Stones cantypically be removed with the use of a good cleaner loader system.

The higher the beet storage clamp thegreater the downward pressure on thebeet and the better the clamp compactionand anaerobic ensiling process. Clamp willreduce in height over time, for example, a 7m high clamp will sink to approx. 4-5m in height over several weeks. Within reason,the greater the height of a clamp the better the condition of the ensiled beet.

Liquor runoff will begin almost immediately.This will comprise between 15% and 40%of the crushed beet value. Ensuring thisrunoff is captured and utilised will bebeneficial as well as reducing pollution.

Hydrolysis Acidogenesis Acetogenesis Methanogenesis


Ensiled Beet

Fresh Beet


Volu

me

of r

unof

f (m

3 )Liquid runoff from 5,000t energy beet clamp

10

0

30

50

60

40

20

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76

Days after clamping

Large volumes run off initially, but thisdecreases over time until a low and stablevolume of liquor is produced. The abovechart, taken from a 5,000t clamp,demonstrates a typical pattern of liquidrunoff measured in m3 per day and doesnot include the effects of rainfall.

Plastic sheeting can be used on the side of the beet clamp to help with theensiling process and ensure capture ofliquid runoff.

The clamp is best sealed with two layers of plastic sheeting with an additional outerprotective layer to prevent bird and pestdamage to the ensiled clamp. Weightsneed to be placed around the base of the clamp and preferably across the top of the clamp to help prevent wind lift and exposure to oxygen.

The clamp will initially billow out as existing oxygen is respired and an oxygen free environment is created.

It will then slump and reduce in height as liquid runoff occurs and the clampconsolidates on itself. The beet will ensilevery quickly, typically within 10-14 days,reaching a steady and preserved state.

Beet will compact tightly together to provide good long-term ensilingconditions. This packing also allows for a stable clamp which holds together,reducing the risk of collapse. It alsoprovides a solid and stable face fromwhich to take the feedstock.

Ensiled beet is preserved perfectly. Storagecan be indefinite as long as the clampmaintains an oxygen free state. This allows for year-round feeding of beet intothe AD plant.

Beet is best chopped into matchbox sizepieces or smaller, prior to feeding into theAD plant. This will increase the surfacearea of the beet accessible for bacteriaand enable faster digestion.




KWS has been developing new beetvarieties for biogas for the last 3-4 years.Its research and development team havefound a direct correlation between drymatter and biogas yield.

These varieties have 11-12% higher dry matter yields than standard beet forsugar production and hence produce a correspondingly higher methane yield.

As with maize the key overall goal is to produce as much dry matter perhectare as possible. There are cleardifferences in breeding goals for energybeet compared to sugar beet – these are detailed in the following table.

KWS Breeding Programme Wholecrop Hybrid Rye

Geographic PotentialHybrid rye is highly robust and will copewith most situations, especially droughtprone conditions. However, maximumyields come from regions with higherrainfall and heavier soils and here rye is a good biogas crop alternative for usewhere maize is not tenable.

Rye also fits well within an energy beetrotation. It can be planted relatively late

and in some situations could be takenearly to allow second cropping with energy beet, providing a double biogascrop opportunity.

On the continent rye has been harvestedearly in April or May prior to double-cropping land with short season maize –though the potential of this approach hasyet to be fully tested in the UK.

Beet Breeding Goals

Sugar Beet Energy Beet

Sugar Content Dry Matter Yield

White Sugar Yield Dry Matter Content

Impurities Methane Yield

Common Breeding Goals

Bolting resistance

Rhizomania resistance

Beet cyst nematode resistance

Dirt Tare


Easy to manage – low input feedstock Lower methane yield per hectare

High wholecrop yields

Ideal ‘maize alternative’ for drought prone regions

Can be drilled late after maize or beet

Could allow double-cropping

Relatively fast retention time

Improves gaseous output from maize

Higher DM content than maize or beet



Energy HybridMaize Rye

Fresh Weight 60 35Yield (t/ha)

Dry Matter % 27-31 33-36

Biogas Yield 200 200m3/t (Fresh)

Methane Conversion 53% 54%

Methane Yield m3/t (Fresh) 105 108

Methane Yield m3/ha 6300 3780

Energy Potential


Hybrid rye is a useful substrate that can be used all year round in the biogasplant. It can be used to balance the highproductivity of energy beet or maizesubstrates, providing an alternativenutrient source for the bacteria in thedigester and stabilising gas output.

In this respect, used alongside maize, it has a synergistic effect in the biogasplant by increasing the gaseous yield, as it increases the length of time for themaize to produce methane in the digester.

By mixing 25% hybrid rye with 75% maize, plant managers can increasegaseous output by nearly 20% more than they can from maize used on its own.However, combined gaseous yielddeclines when the proportion of rye used rises over this level.

95

90

110

115

105

100

Maize

85%

Maiz

e

15%

Rye

75%

Maiz

e

25%

Rye

65%

Maiz

e

35%

Rye

Relative Biogas Yield (Maize at 100%)

Hybrid rye also works well within thebiogas rotation, complementing othercrops. Because it is harvested in thesummer, it can also be stored within empty maize or beet clamps.

Early harvesting when the crop is at 30-35% dry matter produces the best gas yields and reduces costs comparedto rye produced for grain.

As a relatively low input crop, hybrid rye combines high fresh weight yields(around 35t/ha) and offers a higher drymatter content over both beet and maize. Grown and used alongside maize, wholecrop hybrid rye offers an earlier harvest and significant rotational advantages.

Compared to any other winter cereals,hybrid rye is extremely versatile. It hasextreme winter hardiness and tolerance to very late autumn sowing as it tillersstrongly and has strong early growth.

The grain is full of energy and a good feed source for bacteria with a highgaseous output.

Data source: IBS GmbH and KWS Lochow GmbH

Variety SelectionKWS’ experience is that hybrid rye offersgreater potential than all other cereals. Incertain areas this can compete with maize.

The new hybrid ryes being developed can deliver fresh weight yields as high as40t/ha, giving a biogas output of 4320m3/ha compared to conventionally bredrye at around 3000 m3/ha.

Our hybrid rye breeding programmefocuses on high tillering types that producea dense plant population. These varietiesensure fast early growth, productionstability and consistent field performancewith high dry matter yields.

KWS has also focused on providingvarieties that can give a fast turnaround in the rotation – in some situations allowingan early harvest in mid May and thepossibility of twin cropping with an energybeet or maize crop in the same season.

The new generation hybrid ryes have the potential to provide growers withsignificantly higher yields than traditionallybred material.

Yie

ld (t

/ha)

Hybrid Rye - yield progression over time

13

12.5

15

13.5

14

15.5

14.5

ConventionalHybrid

Data source: KWS Lochow GmbH

AgronomicsRye can be sown late (until the end ofOctober at 280-300 seeds sq/m) and hasa well developed root system that extractsnutrients and water from greater soildepths than most cereals. This minimisesN-loss during the winter and can also help minimise soil erosion.

Use a maximum of 100kg/ha N applying40% at the start of vegetative growth andthe remaining 60% at tillering. Agrochemicalinputs are minimal. Compared to ryegrown for grain just one fungicide (focusingon brown rust) and one PGR (unless onheavy soils) may be all that is required.


Drill Timing Date Seed Rate m2

Early Mid to late 170-190September

Medium October 200-230

Late November 240-260onwards



Nutrient Use


However, maximum dry matter andsubsequent biogas production comesfrom ensiling when the grain is at the milkyripe stage. Leaving the crop to maturethrough to June and cutting at milkydough stage can double biogas yieldscompared to cutting at ear emergence.

Rye v Triticale Compared to triticale, rye produces more straw and similar grain yields. For this reason, its higher biomasspotential makes it a better option for use in biogas production.

Harvest/Storage Harvesting at the late milky ripe to earlydough ripe stage provides a dry matter of around 32-38% (max. 40%) and a grain-straw ratio of 1:1.

In order to achieve optimum mechanicalshredding of the whole crop shreddersequipped with grain crackers whose rollerscan be operated at different speeds (up to 60%) should be used. The aim is toexpose as much of the crop to lactic acidbacteria enabling them to propagaterapidly. This will also improve the efficiencyof any ensiling agent.

As the rye stalks are essentially hollow, a lot of oxygen is brought into the silage.For this reason, the shredder should beset to achieve chop lengths of between 6 and 10mm for best results. This will helpachieve a bulk density of more than 230kgof dry substances per m3 after intensivecompacting in the clamp.

Relatively hot harvest conditions can result in the growth of a number of micro-organisms that have a negative effect on the silage leading to high energy loss during storage and potentialaccumulation of toxic by-products in the clamp. A suitable ensiling agent willreduce the natural growth of lactic bacteria in the plant.


Ryegrass

Geographic LimitationsThe relatively wet temperate climate of the UK favours the growth of grass and it is suited to all areas of the UK.

Grass growth starts when temperaturesreach 5°C, and is most vigorous in thewarm wet conditions that are typical of the April, May and June period acrossmost Western and Northern regions of the UK.

AgronomicsMixture selection depends upon thedesired performance of the crop andlength of the rotation.

Fast establishing ryegrass mixtures willprovide good yields over one year ofproduction. They are high yielding sownearly in the spring and allow multiple cutsin the same year. Generally, Italian ryegrasswill provide a ley suitable for cutting over 12-18 months, whereas, perennialryegrass will produce a longer term 2-3year ley.

Optimum establishment will be achievedby sowing at 30-45kg/ha of the selectedmix into a fine, but firm, warm and moistseedbed no deeper than 6mm. Rollinghelps to ensure good seed to soil contact.Grass germinates at 5ºC.

While weed control is not as critical as it is in silage used for stock feed, a 20%dock infestation will cut grass yields by20%, so aim to keep these and otherpernicious weeds such as thistles andnettles down to a minimum.

Control leatherjackets and frit fly – frit fliesemerge in late August/early September, so can be particularly damaging in newsown leys.

CuttingWhen cutting, stubble lengths should beset at a minimum of 7cm. Take care not to contaminate the silage with soil whichwill cause problems in the digester.

Stage of Harvest Dry Biogasmaturity Time Matter Yield

(%) m3/t(Fresh)

Ear tip Beginning <20% <100of May

Flowering Beginning 20-25% 130-160of June

Grain at Mid June 30-35% 200-230milky ripe stage


3-4 cuts can be taken Requires multiple cutting which can drive up overall costs

Consider as an ‘opportunity crop’ if available

N/ha P/ha K/ha Growth Regulator

Light soils Heavy soils

Growth stage 25 60-80kg

Growth stage 31 30-40kg 1.5-1.8l/ha 1.5-1.8l/ha

Growth stage 37 30-40kg 0.5l/ha

Total 120-160kg 110kg max 130kg max



SummaryUK biogas producers can miximise their output by establishing a cropping mix thatprovides a range of feedstocks to secure high gaseous output, which is also sustainablewithin the farm rotation.

Maize, wholecrop cereals and energy beet have the greatest potential within the majorityof UK conditions. While maize is less tenable in the far north of the UK, wholecrop cerealscan provide a suitable alternative.

Notes



Contact usAs the UK industry develops, KWS will continue to introduce a wide range of material to suit ourconditions. Our bioenergy team would be happy to talk to you about your requirements and makecertain you get the best from your crops and biogas operation.

For further information please contact:

John BurgessMaize Product ManagerTel: 01763 207309 Mobile: 07766 258264E.mail: [email protected]

Simon WithefordSugar Beet Product ManagerTel: 01763 207304 Mobile: 07717 844441E.mail: [email protected]

For a more hands on experience of our energycrop portfolio why not visit our ProductDevelopment Field at Thriplow, where you cansee all of our crops in rotational situations.

KWS UK LTD56 Church StreetThriplow, Nr RoystonHertfordshire SG8 7RETel: +44 (0) 1763 207300Fax: +44 (0) 1763 207310E.mail: [email protected]


22589 Biogas in Practice AW:1 - Aylsham Growers Renewables · 2013-04-26 · KWS funds what is...

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Transcript of 22589 Biogas in Practice AW:1 - Aylsham Growers Renewables · 2013-04-26 · KWS funds what is...